1. Field of the Invention
The present invention relates generally to prism and target assemblies such as those employed in surveying, civil engineering and the like for use in measuring distances and more specifically to an improved combined sighting target and prism assembly in which a relatively large target serves the dual function of visual target and structural support for the prism housing.
2. Prior Art
Retro-reflective prism assemblies for use in surveying and civil engineering in conjunction with laser range finding instrumentation for measuring distances is well-known in the art. In addition, the use of targets in close proximity to such retro-reflective prism assemblies for enabling easy sighting of the prism assembly from a long distance for alignment of the laser optics and the prism assembly, is also well-known in the art. In more recent years there has been a commercialization of small prism assemblies for use at shorter distances such as up to one thousand yards. Typically, such smaller prism assemblies have a diameter of approximately 11/2 inches as compared to more conventional prism assemblies having diameters of approximately 3 inches. This reduction in the size of prism assemblies for use at smaller distances has greatly enhanced the convenience of distance measurement in the field by providing pocket size prism assemblies which may be more conveniently carried and more conveniently utilized. One disadvantage however of such a decrease in the size of the retro-reflective prism assembly components is that in order to connect the prism assembly to a suitable sighting target in a conventional manner, it has been necessary to also reduce the size of the sighting target. This latter size reduction makes it more difficult for the initial alignment of the laser optics and the prism assembly and tends to generally defeat the function of the sighting target.
There is therefore a need for providing a sighting target for a smaller retro-reflective prism assembly which permits the user to exploit the advantages of smaller prism assembly components, but without requiring a commensurate decrease in the size of the sighting target which would otherwise tend to defeat the sighting target function which is to provide a readily observable target with which to align the optics of the system for distance measurement.